Reference is hereby made to commonly-assigned, copending patent applications having the following titles, serial numbers, and docket numbers:
xe2x80x9cMethod of Producing Exchange Coupling Film and Method of Producing Magnetoresistive Sensor by Using the Exchange Coupling Filmxe2x80x9d, application Ser. No. 09/833,306, docket number: 9281-3954.
xe2x80x9cExchange Coupling Film and Electroresistive Sensor Using the Samexe2x80x9d, application Ser. No. 09/833,756, docket number: 9281-3955.
xe2x80x9cExchange Coupling Film and Electroresistive Sensor Using the Samexe2x80x9d, application Ser. No. 09/834,105, docket number 9281-3957.
The present invention relates to methods of producing an exchange coupling film having an antiferromagnetic layer and a ferromagnetic layer, wherein the direction of magnetization of the ferromagnetic layer is fixed by an exchange coupling magnetic field produced at the interface between the antiferromagnetic layer and the ferromagnetic layer. More particularly, the present invention relates to methods of producing an exchange coupling film that provides a large exchange coupling magnetic field, to methods of producing a magnetoresistive sensor (spin-valve-type thin-film device, AMR device), and to methods of producing a thin-film magnetic head using the magnetoresistive sensor.
A spin-valve-type thin-film device is a kind of GMR (Giant Magnetoresistive) device which makes use of a giant magnetoresistive effect, which is used for detecting recording magnetic fields from a recording medium such as a hard disk.
The spin-valve-type thin-film device, relative to other GMR devices, has advantageous features such as simplicity of structure and ability to vary its magnetic resistance even under a weak magnetic field.
The simplest form of the spin-valve-type thin-film device includes an antiferromagnetic layer, a pinned magnetic layer, a non-magnetic intermediate layer, and a free magnetic layer.
The antiferromagnetic layer and the pinned magnetic layer are formed in contact with each other. The direction of the pinned magnetic layer is aligned in a single magnetic domain state and fixed by an exchange anisotropic magnetic field produced at the interface between the antiferromagnetic layer and the pinned magnetic layer.
The magnetization of the free magnetic layer is aligned in a direction which intersects the direction of magnetization of the pinned magnetic layer, by the effect of bias layers that are formed on both sides of the free magnetic layer.
Alloy films such as an Fexe2x80x94Mn (Iron-Manganese) alloy films, Nixe2x80x94Mn (Nickel-Manganese) alloy films and Ptxe2x80x94Mn (Platinum-Manganese) alloy films are generally usable materials for the antiferromagnetic layer. Of these, Ptxe2x80x94Mn alloy films are attracting attention for advantages such as high blocking temperature, superior corrosion resistance, and so forth.
It has been found that when a Ptxe2x80x94Mn alloy film is used for the antiferromagnetic layer, the antiferromagnetic layer deposited has a face-centered cubic crystalline structure in which atoms are irregularly aligned.
In order to develop the proper intensity of exchange coupling magnetic field between the antiferromagnetic layer and a ferromagnetic layer, it is necessary to transform the crystalline structure of the deposited antiferromagnetic layer from a face-centered cubic disordered lattice into a CuAuxe2x80x94I type face-centered cubic ordered lattice. This transformation is caused by effecting a heat-treatment.
In addition, it has been found that in a bulk type Ptxe2x80x94Mn alloy, a CuAuxe2x80x94I type face-centered lattice is easiest to obtainxe2x80x94and, therefore, antiferromagnetic properties are easiest to achievexe2x80x94when the at % ratio between Pt and Mn is 50:50. Thus, to measure the intensity of an exchange coupling magnetic field developed between the antiferromagnetic layer and the ferromagnetic layer, the present inventors used a Ptxe2x80x94Mn alloy film with an at % ratio between Pt and Mn of approximately 50:50 as an antiferromagnetic layer in a spin-valve-type thin-film device.
It was found, however, that a sufficient intensity of the exchange coupling magnetic field could not be obtained, despite an ideal bulk type composition ratio of Pt to Mn. While it is not the Applicants"" desire to be bound by a particular theory, it is believed that this results from an insufficient transformation of the crystalline structure of the antiferromagnetic layer from a disordered lattice into an ordered lattice even following a heat-treatment.
Accordingly, an object of the present invention is to provide a method of producing an exchange coupling film having a large exchange anisotropic magnetic field by using an antiferromagnetic material comprising an element X (X is a platinum group element) and Mn as the antiferromagnetic layer, a method of producing a magnetoresistive sensor using the exchange coupling film, and a method of producing a thin-film magnetic head using the magnetoresistive sensor, thereby overcoming the above-described problems.
In accordance with a first aspect of the present invention, there is provided a method of producing an exchange coupling film comprising: forming a first antiferromagnetic layer which contacts a ferromagnetic layer at an interface therebetween from antiferromagnetic materials comprising an element X and Mn, and forming a second antiferromagnetic layer which contacts the first antiferromagnetic layer from antiferromagnetic materials comprising an element X and Mn, wherein the element X comprises one or more elements selected from the group consisting of Pt, Pd, Ir, Rh, Ru and Os, such that the second antiferromagnetic layer has a smaller composition ratio of the element X than the first antiferromagnetic layer; and effecting a heat-treatment whereby an exchange coupling magnetic field at the interface between the first antiferromagnetic layer and the ferromagnetic layer is developed.
As described above, when the at % ratio between Pt and Mn is 50:50, the crystalline structure is transformed into an ordered lattice, and antiferromagnetic properties are mostly exhibited. However, since it is difficult to create a non-aligned state at the interface between the antiferromagnetic layer and the ferromagnetic layer, transformation from a disordered lattice into an ordered lattice is not sufficiently effected by the heat-treatment; as a result, an insufficient exchange coupling magnetic field is obtained. The term xe2x80x9cnon-aligned statexe2x80x9d means that atoms in the antiferromagnetic layer and atoms in the ferromagnetic layer differ in positional relationship and do not provide a one-to-one correspondence.
On the other hand, a Pt content below 50 at % makes it difficult to transform the crystalline structure into an ordered lattice by heat-treatment, and to achieve antiferromagnetic properties. At the same time, an aligned state at the interface between the antiferromagnetic layer and the ferromagnetic layer is strong, such that the exchange coupling magnetic field is considerably reduced.
On the one hand, a Pt content above 50 at % facilitates creation of a non-aligned state at the interface between the ferromagnetic layer and the antiferromagnetic layer but, on the other hand, makes it difficult to transform the crystalline structure into an ordered lattice by heat-treatment and to achieve antiferromagnetic properties. As a result, the exchange coupling magnetic field is considerably reduced.
Accordingly, when depositing the antiferromagnetic layer prior to heat-treatment, a thin layer of a Ptxe2x80x94Mn alloy with a high Pt content (referred to as the xe2x80x9cfirst antiferromagnetic layerxe2x80x9d) is formed on the side of the antiferromagnetic layer adjacent to the ferromagnetic layer. In addition, a Ptxe2x80x94Mn alloy film having a composition ratio that is easily transformed from a disordered lattice into an ordered lattice upon heat-treatment (referred to as the xe2x80x9csecond antiferromagnetic layerxe2x80x9d), and having a thickness larger than that of the first antiferromagnetic layer, is formed on the ferromagnetic layer through the intermediary of the first antiferromagnetic layer.
While it is not the Applicants"" desire to be bound by a particular theory, it is believed that during the deposition and prior to heat-treatment, the high Pt content of the first antiferromagnetic layer eliminates the influence of crystalline structure and the like of the ferromagnetic layer at the interface between the ferromagnetic layer and the first antiferromagnetic layer. The second antiferromagnetic layer is properly transformed by heat-treatment, and a diffusion of component takes place in the first and second antiferromagnetic layers when the transformation is started. As a result, the Pt content varies and the deposited composition prior to heat-treatment is transformed into a composition which is easy to transform from a disordered lattice into an ordered lattice. Thus, the transformation is caused in the first antiferromagnetic layer.
More specifically, according to the production method heretofore described, the first antiferromagnetic layer which has a high Pt content and which is not influenced by the crystalline structure and the like of the ferromagnetic layer at the interface between the ferromagnetic layer and the first antiferromagnetic layer is provided between the second antiferromagnetic layer which is formed from an ideal composition for easily obtaining a CuAuxe2x80x94I type face-centered cubic ordered lattice and the ferromagnetic layer. As a result, the antiferromagnetic layers can be sufficiently transformed from a disordered lattice into an ordered lattice while maintaining the non-influenced state, thereby making it possible to obtain a greater exchange coupling magnetic field than heretofore.
In accordance with the present invention, the second ferromagnetic layer is formed from an antiferromagnetic material containing an element X and Mn, such that the composition ratio of the element X of the second antiferromagnetic layer is smaller than that of the first ferromagnetic layer. This allows the second antiferromagnetic layer to be properly transformed from a disordered lattice into an ordered lattice upon heat-treatment, thereby making it possible to obtain a large exchange coupling magnetic field.
Preferably, the lattice constant of the first antiferromagnetic layer is different from the lattice constant of the ferromagnetic layer at at least a part of the interface between the first antiferromagnetic layer and the ferromagnetic layer. In addition, the crystal orientation of the first antiferromagnetic layer may be different from the crystal orientation of the ferromagnetic layer at at least a part of the interface between the first antiferromagnetic layer and the ferromagnetic layer.
In accord with the present invention, a difference in crystal orientation is created between the first antiferromagnetic layer and the ferromagnetic layer after deposition.
For instance, when the (111) plane of the ferromagnetic layer has been preferentially oriented in a direction parallel to the interface, the (111) plane of the antiferromagnetic layer either has a smaller degree of orientation than that of the (111) plane of the ferromagnetic layer, or is altogether unoriented.
Alternatively, when the (111) plane of the antiferromagnetic layer has been preferentially oriented in a direction parallel to the interface, the (111) plane of the ferromagnetic layer either has a smaller degree of orientation than that of the (111) plane of the antiferromagnetic layer, or is altogether unoriented.
In another alternative, the degrees of orientation of the (111) faces of the antiferromagnetic layer and the ferromagnetic layer either have reduced degrees of orientation, or are altogether unoriented, with respect to the directions parallel to the interface between the antiferromagnetic layer and the ferromagnetic layer 3. Crystal planes other than the (111) planes are preferentially oriented with respect to the directions parallel to the interface, thereby creating a difference in crystal orientation between the antiferromagnetic layer and the ferromagnetic layer.
The degree of crystal orientation is controllable by varying the order of deposition of the layers, or by varying conditions such as presence or absence of an underlying layer, composition ratio, electrical power and gas pressure during sputtering.
Preferably, a non-aligned state is created at at least a part of the interface between the first antiferromagnetic layer and the ferromagnetic layer. It is possible to diminish a restraint force produced by the crystalline structure, etc. of the ferromagnetic layer on the interface by obtaining such a non-aligned state.
It is possible to facilitate creation of the non-aligned state at the interface between the antiferromagnetic layer and the ferromagnetic layer and to obtain a greater exchange coupling magnetic field than heretofore, by creating a difference in lattice constant or crystal orientation at the interface between the antiferromagnetic layer and the ferromagnetic layer, as described above.
In addition, it is preferred that at least a first antiferromagnetic layer which contacts a ferromagnetic layer at an interface therebetween, and a second antiferromagnetic layer which contacts the first antiferromagnetic layer are formed, the first and second antiferromagnetic materials comprising an element X, an element Xxe2x80x2 and Mn, wherein the element X is one or more elements selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Os, and the element Xxe2x80x2 comprises one or more elements selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element, such that a composition ratio of the elements Xxe2x88x92Xxe2x80x2 of the second antiferromagnetic layer is smaller than a composition ratio of the elements X+Xxe2x80x2 of the first antiferromagnetic layer. This also makes it possible to provide an exchange coupling film which can provide a larger exchange coupling magnetic field than conventional exchange coupling magnetic fields.
When the antiferromagnetic layer is formed from an Xxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, it is preferable that the element Xxe2x80x2 be an element which would invade the interstices of the space lattice composed of the element X and Mn or an element which would substitute for a portion of the lattice points of the crystalline lattice constituted by Mn and the element X. This can enhance the lattice constants of the first and second antiferromagnetic layers. In particular, creation of a non-aligned state at the interface between the first antiferromagnetic layer and the ferromagnetic layer is facilitated, thereby making it possible to obtain a large exchange coupling magnetic field.
Preferably, the composition ratio of the element X or the composition ratio of the elements X+Xxe2x80x2 of the second antiferromagnetic layer is not less than 44 at % and not more than 57 at %, more preferably not less than 46 at % and not more than 5 at %.
Composition ratios within this range can properly transform from a disordered lattice into an ordered lattice upon heat-treatment, thus affording a large exchange coupling magnetic field.
Preferably, the composition ratio of the element X or the composition ratio of the elements X+Xxe2x80x2 of the first antiferromagnetic layer is not less than 53 at % and not more than 65 at %. Results of experiments which will be described hereinbelow show that composition ratios of the element X or composition ratios of the elements X+Xxe2x80x2 of the first antiferromagnetic layer within this range can provide an exchange coupling magnetic field of 7.9xc3x97104 A/m or greater.
In accordance with the present invention, it is preferred that the composition ratio of the element X and the composition ratio of the elements X+Xxe2x80x2 of the first antiferromagnetic layer are not less than 55 at % and not more than 60 at %, so that a greater exchange coupling magnetic field is obtained.
In accordance with the present invention, it is also preferred that the second antiferromagnetic layer has a thickness of 70 xc3x85 or greater. It has been found that an exchange coupling magnetic field of 7.9xc3x97104 A/m or greater can be obtained when the second antiferromagnetic layer has a thickness within this range.
It is also preferred that the first antiferromagnetic layer has a thickness not smaller than 3 xc3x85and not greater than 30 xc3x85. It has been found that an exchange coupling magnetic field of 7.9xc3x97104 A/m or greater can be obtained when the first antiferromagnetic layer has a thickness falling within this range.
In accordance with the present invention, it is preferred that the first and second antiferromagnetic layers are formed by a sputtering process, and that the sputtering gas pressure at which the first antiferromagnetic layer is formed is lower than the sputtering gas pressure at which the second antiferromagnetic layer is formed. This makes it possible to reduce the element X in the composition ratio of the elements X+Xxe2x80x2 of the second antiferromagnetic layer to be smaller than the element X in the composition ratio of the elements X+Xxe2x80x2 of the first antiferromagnetic layer.
In accordance with a second aspect of the present invention, there is provided a method of producing an exchange coupling film which develops an exchange coupling magnetic field at an interface between an antiferromagnetic layer and a ferromagnetic layer, the method comprising: forming the ferromagnetic layer; forming the antiferromagnetic layer on the ferromagnetic layer by a sputtering process in which an element X and Mn are used as sputtering targets, wherein the element X comprises one or more elements selected from the group consisting of Pt, Pd, Ir, Rh, Ru, and Os, and wherein a sputtering gas pressure is progressively increased in a direction away from the ferromagnetic layer during the forming of the antiferromagnetic layer, such that the composition ratio (atomic percent) of the element X is reduced in a direction away from the ferromagnetic layer; and effecting a heat-treatment after forming the antiferromagnetic layer and the ferromagnetic layer, such that an exchange coupling magnetic field is developed at the interface between the antiferromagnetic layer and the ferromagnetic layer.
Preferably, a difference in lattice constant is created between the antiferromagnetic layer and the ferromagnetic layer at at least a part of the interface between the antiferromagnetic layer and the ferromagnetic layer.
Alternatively, a difference in crystal orientation may be created between the antiferromagnetic layer and the ferromagnetic layer at at least a part of the interface between the antiferromagnetic layer and the ferromagnetic layer.
It is also preferred that a non-aligned state is created at at least a part of the interface between the antiferromagnetic layer and the ferromagnetic layer.
In this method according to the present invention, it is preferred that the antiferromagnetic layer is formed by a sputtering process in which elements X+Xxe2x80x2 and Mn are used as sputtering targets, wherein the element Xxe2x80x2 comprises one or more elements selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N, Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb and a rare earth element, and wherein the sputtering gas pressure is progressively increased in a direction away from the ferromagnetic layer 3 during the forming of the antiferromagnetic layer, such that the composition ratio (atomic percent) of the elements X+Xxe2x80x2 is reduced in a direction away from the ferromagnetic layer.
In addition, the element Xxe2x80x2 may preferably be an element which would invade the interstices of a space lattice composed of the element X and Mn or an element which would substitute for a portion of the lattice points of a crystalline lattice constituted by Mn and the element X.
In an alternative embodiment in accordance with the present invention, the antiferromagnetic layer may be composed of a single layer rather than the first and second ferromagnetic layers in the as-deposited state. The production method is characterized in that the composition ratio (at %) of the element X or the composition ratio (at %) of the elements X+Xxe2x80x2 of the antiferromagnetic layer is progressively decreased in a direction away from the ferromagnetic layer during deposition of the antiferromagnetic layer, while the sputtering gas pressure is changed. During deposition, an unaligned state is created at at least a part of the interface between the antiferromagnetic layer and the ferromagnetic layer. In addition, a difference in lattice constant and a difference in crystal orientation are created.
By effecting a heat-treatment, deformation from a disordered lattice to an ordered lattice is started in a region of the antiferromagnetic layer away from the interface. When the transformation is promoted, the elements actively diffuse through the antiferromagnetic layer, and the composition ratio (at %) of the element X or the composition ratio (at %) of the elements X+Xxe2x80x2 is decreased near the interface. As a result, proper transformation from a disordered lattice into an ordered lattice is effected.
Thus, in accordance with the present invention, the antiferromagnetic layer is not influenced by the restraint force of the crystalline structure and the like of the ferromagnetic layer at the interface between the ferromagnetic layer and the antiferromagnetic layer. Even in the deposition described above, the overall antiferromagnetic layer can be properly transformed from a disordered lattice into an ordered lattice, making it possible to obtain a greater exchange coupling magnetic field than was heretofore possible.
Preferably, the composition ratio of the element X or the elements X+Xxe2x80x2 of the antiferromagnetic layer to the total composition ratio (100 at %) of all the elements constituting the antiferromagnetic layer is not less than 44 at % and not more than 57 at %, more preferably not less than 46 at % and not more than 55 at % in a region of the antiferromagnetic layer opposite to the interface.
In addition, it is preferable that the composition ratio of the element X or the elements X+Xxe2x80x2 of the antiferromagnetic layer to the total composition ratio (100 at %) of all the elements constituting the antiferromagnetic layer is not less than 53 at % and not more than 65 at %, in the region near the interface between the antiferromagnetic layer and the ferromagnetic layer. It has been confirmed that a composition ratio within this range can provide an exchange coupling magnetic field of 7.9xc3x97104 A/m or greater.
It is more preferable that the composition ratio of the element X or the elements X+Xxe2x80x2 of the antiferromagnetic layer to the total composition ratio (100 at %) of all the elements constituting the antiferromagnetic layer is not less than 55 at % but not more than 60 at %, in the region of the antiferromagnetic layer near the interface.
In addition, the antiferromagnetic layer may preferably have a thickness of 73 xc3x85 or greater.
The methods of producing an exchange coupling film described above can be used for the production of a variety of types of magnetoresistive sensors.
The present invention also provides a method of producing a single-spin valve type magnetoresistive sensor comprising an antiferromagnetic layer, a pinned magnetic layer in contact with the antiferromagnetic layer which has a direction of magnetization fixed by an exchange anisotropic magnetic field with the antiferromagnetic layer, a non-magnetic intermediate layer between the pinned magnetic layer and a free magnetic layer, and a bias layer which aligns the direction of magnetization of the free magnetic layer in a direction that intersects the direction of magnetization of the pinned magnetic layer. The method comprises forming the antiferromagnetic layer and the pinned magnetic layer in contact therewith from the exchange coupling film described above.
The present invention also provides a method of producing a single-spin valve type magnetoresistive sensor comprising an antiferromagnetic layer, a pinned magnetic layer in contact with the antiferromagnetic layer which has a direction of magnetization fixed by an exchange anisotropic magnetic field with the antiferromagnetic layer, a non-magnetic intermediate layer between the pinned magnetic layer and a free magnetic layer having an upper side and a lower side, and an antiferromagnetic exchange bias layer on either the upper side or the lower side of the free magnetic layer, the antiferromagnetic exchange bias layer comprising a plurality of portions spaced from each other in the track width direction, the method comprising forming the exchange bias layer and the free magnetic layer from the exchange coupling film described above, such that the free magnetic layer is magnetized in a fixed direction.
The present invention also provides a method of producing a dual-spin valve type magnetoresistive sensor comprising a first antiferromagnetic layer; a first pinned magnetic layer overlying the first antiferromagnetic layer; a first non-magnetic layer overlying the first pinned magnetic layer; a free magnetic layer overlying the first non-magnetic layer; a second non-magnetic layer overlying the free magnetic layer; a second pinned magnetic layer overlying the second non-magnetic layer; a second antiferromagnetic layer overlying the second pinned magnetic layer, the first and second antiferromagnetic layers serving to fix directions of magnetization of the first and second pinned magnetic layers by exchange anisotropic magnetic fields; and a bias layer which aligns a direction of magnetization of the free magnetic layer to a direction that intersects the directions of the first and second pinned magnetic layers, the method comprising forming at least one of the first and second antiferromagnetic layers, and at least one of the first and second pinned magnetic layers in contact therewith, from the exchange coupling film described above.
Furthermore, the present invention provides a method of producing an AMR device comprising a magnetoresistive layer having an upper side and a lower side and a soft magnetic layer, the magnetoresistive layer and the soft magnetic layer being superposed through the intermediary of a non-magnetic layer, and an antiferromagnetic layer on the upper side or the lower side of the magnetoresistive layer, the antiferromagnetic layer comprising a plurality of portions spaced apart in the track width direction, the method comprising forming the antiferromagnetic layer and the magnetoresistive layer from the exchange coupling film described above.
A method in accord with the present invention for producing a thin-film magnetic head comprises forming, on each of the upper side and the lower side of one of the magnetoresistive sensors heretofore described, a shield layer across a gap layer.
A magnetoresistive sensor formed by using the large exchange coupling magnetic field has excellent thermal stability. The magnetoresistive sensor can be properly operated even at high ambient temperature during driving, and a large resistance variation ratio can be maintained.